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The present invention relates to a vehicular lamp of a type employing an LED light source, and more particularly to such a vehicular lamp which is constructed so as to radiate light by indirect illumination.
Recently, vehicular lamps provided with an LED light source have frequently been employed. As described in Japanese Patent Application Laid-Open No. 11-306810, a lamp has been developed which provides a soft lighting effect using an indirect illumination technique whereby the LED light source is arranged so as not to be visible from the front of the lamp. To achieve this effect, the lamp employs a Fresnel lens together with the LED light source.
As shown in FIG. 10, such a lamp is structured such that light from an LED light source 102, which is arranged facing upward, is formed into an upward directed parallel light flux by a Fresnel lens 104 provided near the upper side of the LED light source 102, and the parallel light flux from the Fresnel lens 104 is then directed in a diffused manner toward the front of the lamp by a reflector 106. The reflector 106 of the vehicular lamp is formed with a stepped shape whereby the reflecting surface 106a thereof is divided into a plurality of segments arranged at a uniform interval Hxe2x80x2 with respect to the vertical direction (the direction of the optical axis Axxe2x80x2 of the Fresnel lens 104), and a reflective element 106s reflecting the parallel light flux in a diffused manner toward the front of the lamp and a step portion 106r extending in the vertical direction are provided in each of the segments.
In the conventional vehicular lamp described above, since the reflector 106, which is formed generally as a flat plate, is inclined at a predetermined angle with respect to the direction of the optical axis Axxe2x80x2, and the widths of the reflective elements 106s in the longitudinal direction of the lamp are all the same value wxe2x80x2 (the heights of the reflective elements 106s in the vertical direction are all the same width hxe2x80x2), problems as will now be described occur.
Since the light emitted by the LED light source 102 has a luminous intensity distribution I wherein the maximum luminous intensity occurs in the directly frontward direction and the luminous intensity is reduced as the angle with respect to the directly frontward direction increases, the light flux per unit area of the Fresnel lens 104 is high in an area near the optical axis Axxe2x80x2 and becomes reduced in peripheral areas. Further, a solid angle per unit area of the Fresnel lens 104 with respect to the LED light source 102 is large in the area near the optical axis Ax and becomes small in the peripheral areas (xcex8axe2x80x2 greater than xcex8bxe2x80x2 greater than xcex8cxe2x80x2 greater than xcex8dxe2x80x2). Accordingly, the light flux per unit area striking the reflective elements 106s in peripheral areas on both of upper and lower sides of the central area near an intersection point Cxe2x80x2 with respect to the optical axis Axxe2x80x2 on the reflecting surface 106a is smaller (xc3x8axe2x80x2 greater than xc3x8bxe2x80x2 greater than xc3x8cxe2x80x2 greater than xc3x8dxe2x80x2) than that striking the reflective elements 106s constituting the central area.
Therefore, when viewing the reflecting surface 106a of the reflector 106 from the front of the lamp when the lamp is lit, while the reflective elements 106s in the central area are seen brightly, the reflective elements 106s constituting the peripheral areas appear dark, so that there is a problem that the overall appearance of the lamp is not as good as desired.
Taking the foregoing into consideration, it is an object of the present invention to provide a vehicular lamp of a type in which light from an LED light source is irradiated by indirect illumination whereby the lamp has an improved appearance when the lamp is lit.
The present invention achieves the above and other objects by providing a lamp of the above-described type but in which the size of each of the reflective elements constituting the reflecting surface of the reflector is determined so as to obtain more uniform illumination.
More specifically, a vehicular lamp according to the present invention comprises an LED light source, a lens for forming light from the LED light source into a parallel light flux, a reflector for reflecting the parallel light flux toward the front of the lamp, and a translucent cover provided in front of the reflector of the lamp, wherein the reflecting surface of the reflector is sectioned into a plurality of segments at a substantially uniform interval with respect to the radiating direction of the parallel light flux, and a reflective element and a step portion are provided in each of the segments, whereby the reflecting surface is formed in a stepped shape, and the width in a longitudinal direction of the lamp of each of the reflective elements is determined such that, compared to a reflective element constituting a central area positioned near an intersection point with respect to a central axis of the parallel light flux on the reflecting surface, reflective elements is peripheral areas on both sides in the radiating direction of the parallel light flux with respect to the central area becomes wider.
The specific structure of the lens is not particularly limited as far as the lens can form the light from the LED light source into a parallel light flux, for example, it is possible to employ a single spherical lens, a combination lens, a Fresnel lens or the like.
The direction of the optical axis of the lens is not limited to a specific direction as far as the direction corresponds to a direction intersecting the longitudinal direction of the lamp, for example, it is possible to set the direction of the optical axis in an upward direction or a lateral direction by making the direction perpendicular to the longitudinal direction of the lamp.
The central axis of the parallel light flux is generally set to be coaxial with the optical axis of the lens; however, it may be set to a direction slightly inclined with respect to the optical axis of the lens. The latter setting can be achieved by arranging the LED light source at a position offset from the optical axis of the lens, providing light deflecting means near the reflector side of the lens, or the like.
As described above, the vehicular lamp according to the present invention is structured such that the reflecting surface of the reflector which reflects the light from the LED light source, made into the form of a parallel light flux by the Fresnel lens, toward the front of the lamp is sectioned into a plurality of segments substantially at a uniform interval with respect to the radiating direction of the parallel light flux. Moreover, a reflective element and a step portion are provided in each of the segments, whereby the reflecting surface is formed in the stepped shape. The width in the longitudinal direction of the lamp of each of the reflective elements is determined such that the reflective elements constituting the peripheral areas on both sides in the radiating direction of the parallel light flux with respect to the central area near the intersection point with the central axis of the parallel light flux on the reflecting surface are wider than the reflective elements constituting the central area. Due to this construction, the following effects are obtained.
That is, as described above, since the light flux per unit area of the parallel light flux reaching the reflecting surface of the reflector from the lens is smaller in the peripheral areas than in the central area of the reflecting surface in the conventional lamp, the reflective elements constituting the central area generally appear bright while the reflective elements constituting the peripheral areas appear more dark when viewing the reflecting surface of the reflector from the front of the lamp when the lamp is lit. On the contrary, according to the present invention, since the width in the longitudinal direction of the lamp of each of the reflective elements is greater for the reflective elements constituting the peripheral areas than for the reflective elements constituting the central area, such a difference in brightness between the reflective elements constituting the central area and the reflective elements constituting the peripheral areas is significantly reduced.
Therefore, the inventive vehicular lamp wherein light from an LED light source is radiated by indirect illumination has an improved appearance when the lamp is lit.
In the lamp structure described above, in the case where the width in the longitudinal direction of the lamp of each of the reflective elements increases as the position of the reflective element increases on both sides in the radiating direction of the parallel light flux from the intersection point between the parallel light flux and the central axis on the reflecting surface, it is possible to make the difference in brightness much smaller between the reflective elements constituting the central area and the reflective elements constituting the peripheral areas.
Moreover, in the case where the width in the longitudinal direction of the lamp of each of the reflective elements is such that the incident light fluxes onto all the reflective elements are substantially equal to each other, the brightnesses of the reflective elements are made uniform over the entire reflecting surface.
Further, in the lamp constructed as described above, in the case where each of the reflective elements is constituted by a curved surface which reflects the parallel light flux from the lens in a diffused manner in both vertical and lateral directions, it is possible to obtain a required lamp light distribution performance even if the cover of the lamp is translucent and generally plain. In the case where the diffused reflection angle of each of the reflective elements is substantially the same, each of the reflective elements will be seen in substantially the same brightness within the same angular range when viewed from an oblique direction with respect to the forward direction of the lamp.
Alternatively, each of the reflective elements can be constituted by a flat plane so as to reflect the parallel light flux from the lens toward the front of the lamp while maintaining the light flux parallel, in which case diffusion lens elements are formed in the translucent cover or the like, thereby diffusing the light in the vertical direction and the lateral direction. Otherwise, the reflective elements may be constituted by a curved surface having curvature only in one direction so as to reflect the parallel light flux from the lens toward the front of the lamp only in one direction in a diffused manner, and diffusion lens elements are formed in the translucent cover or the like, thereby diffusing the light in the direction perpendicular to the above-mentioned one direction.
Further, in the case where the lens is constituted by a Fresnel lens in which a plurality of Fresnel lens elements are formed on the surface on the lens plate on the side of the LED light source, and a plurality of deflection lens elements for emitting the parallel light flux transmitted through the Fresnel lens in a direction inclined at a predetermined angle with respect to the optical axis of the Fresnel lens are formed on the lens plate on the side of the reflector, the following operations and effects can be obtained.
That is, due to limitations on the lamp layout or the like it may be difficult to arrange the reflecting surface of the reflector at a directly frontward position in the direction of the optical axis of the lens. However, in the case where the parallel light flux is emitted in a direction inclined at a predetermined angle with respect to the optical axis of the Fresnel lens, it is possible to radiate the parallel light flux in the same direction in which the reflecting surface is arranged, even if the reflecting surface of the reflector is arranged at a position slightly shifted from the directly frontward position in the direction of the optical axis of the lens. Accordingly, it is possible to increase the freedom of design choice with respect to the shape of the reflector while maintaining the effect of reducing the difference in brightness between the reflective elements constituting the central area of the reflection area and the reflective elements constituting the peripheral areas. Further, it is possible to achieve the effects mentioned above using only a single Fresnel lens.
The vehicular lamp according to the present invention may be structured so as to irradiate only the light from the LED light source via the lens, the reflector and the translucent cover. However, a second lamp unit may be additionally provided. In such a case, the lamp unit may be mounted to the front of the LED light source and the lens of the lamp, and it is possible to make the LED light source and the lens invisible from the front of the lamp, whereby it is possible to improve the appearance of the lamp. In this case, specific structure, type, shape and the like of the second lamp unit are not particularly limited.